Virus like particles (VLPs) consist of viral proteins derived from the structural proteins of a virus, usually in the absence of a viral genome. VLPs have received considerable attention for vaccines, targeted drug delivery, targeted gene delivery, and nanotechnology applications. VLP vaccines that are currently approved by the Food and Drug Administration (FDA) include human papillomavirus and Hepatitis B vaccines, which are very effective at eliciting both T cell and B cell immune responses.
The vast majority of eukaryote-infecting-virus-based VLPs have been synthesized using the insect-cell-based baculovirus expression system or mammalian-cell-based protein expression systems. Although the synthesis of virus-like particles has been attempted in cell-free systems, yields have been extremely low in eukaryotic cell-free systems (Lingappa et al. 2005. Virology 333:114), and assembly has failed in conventional prokaryotic systems (Katanaev et al. 1996. FEBS 397:143).
Virus-like particle (VLP) vaccines are typically comprised of multiple copies of a protein that, when assembled together, mimic the conformation of a native virus. In the currently approved vaccines, the virus coat proteins themselves are the antigen of interest, and thus the virus protein is derived from the pathogen of interest. However, there has also been interest in using a VLP as a carrier for heterologous antigens, e.g. polypeptide antigens.
Encapsidation of exogeneous materials with a VLP has also been explored with viruses produced in cell culture. Loo et al. (2007) J Am Chem. Soc. 129(36):11111-7 report that small nanoparticles conjugated to an origin of assembly RNA sequence were encapsidated by red clover necrotic mosaic virus. In the absence of packageable viral RNA, assembly of retrovirus is still efficient, and the released virus-like particles still contain roughly normal amounts of RNA. It was also found that the retrovirus will non-selectively package mRNAs (Rulli et al. (2007) J. Virol. 81(12):6623-31).
Wu et al. (2005) Nanomedicine 1(1):67-76 report encapsidation of antisense oligonucleotides in MS2 bacteriophage capsid proteins. The oligonucleotides were synthesized as covalent extensions to the translational repressor/assembly initiation signal (TR), a 19 nt stem-loop, of the RNA phage MS2. The VLPs were constructed by soaking the oligonucleotides directly into recombinant RNA-free capsid shells.
Methods of encapsidating entities in VLPs are of great interest, particularly in combination with cell-free protein synthesis systems.
Relevant Literature
DuBois et al. U.S. Pat. No. 5,677,124, 1997; Wilson and Hwang-Lee, U.S. Pat. No. 5,443,969, 1995; Pasloske et al. U.S. Pat. No. 6,399,307, 2002; Pasloske et al., U.S. Pat. No. 6,214,982, 2001.